Electronic devices are widely used in many types of electronic equipment. One electronic device is the integrated circuit (IC) which may include a silicon or gallium arsenide substrate and a number of active devices, such as transistors, etc. formed in an upper surface of the substrate. It is also typically required to support one or more such ICs in a package that provides protection and permits external electrical connection.
As the density of active devices on typical ICs has increased, dissipation of the heat generated has become increasingly more important. In particular, a relatively large amount of heat may be generated in multi-chip modules (MCMs), microwave transmitters, and photonic devices, for example.
One heat dissipation approach which has been used in a variety of applications, including electronic circuit modules, to provide high thermal transport over long distances is a “heat pipe.” The heat pipe is a sealed system that includes an evaporator, a condenser, an adiabatic region connecting the evaporator and condenser for liquid and vapor transport, and a capillary or wick for circulating cooling fluid therein. Heat pipes enjoy an advantage over other forms of heat regulating devices in that they can transfer heat without the need for a mechanical pump, compressor or electronic controls, which may provide space savings in certain instances.
An example of an MCM which uses a heat pipe is disclosed in U.S. Pat. No. 5,216,580 to Davidson et al. This MCM includes electronic circuit components mounted on one side thereof and a thermal wick mounted on another side. A heat pipe evaporator and condenser assembly is attached to the MCM and wick assembly. Furthermore, a suitable working fluid is introduced into the heat pipe assembly which is then hermetically sealed.
In some electronic device applications, the substrate may comprise plastic. In these applications, the heat dissipation approach may comprise the substrate with a copper body or “coin” directly beneath the IC and extending completely through the substrate. The copper coin transfers thermal energy from the IC through the substrate and out the opposite surface, i.e. out the exposed bottom of the copper coin.
Referring to FIG. 1, a prior art electronic device 400 includes a plastic substrate 401, and a thermally conductive copper coin 404 carried within the plastic substrate. The electronic device 400 includes first and second ICs 402a-402b carried by an upper surface of the plastic substrate 401, and a radio frequency (RF) shield 403 over the upper surface.
Referring to FIG. 2, another prior art electronic device 500 includes a plastic substrate having two stacked layers 501a-501b, and a thermally conductive copper coin 504 carried within the plastic substrate. In this approach, the thermally conductive copper coin 504 is press-fitted or embedded into the plastic substrate. The electronic device 500 includes an IC 502 carried by an upper surface of the plastic substrate.